In ophthalmic surgery, a high viscosity material often called a surgical viscoelastic is injected into the eye as a surgical aid. Viscoelastic materials used in ophthalmic surgery include compositions containing hyaluronic acid, chondroitin sulfate or chemically modified cellulose. Due to the unusual shear thinning or thixotropic properties of such materials, viscoelastics are injectable through a small bore needle or cannula, then recoil to a material providing stiff gel-like properties after injection. A viscoelastic is often injected into the anterior chamber of the eye during cataract surgery to maintain the intraocular space and protect the corneal endothelium from mechanical damage. The injection of viscoelastic is used to dilate tissue spaces such as Schlemm's canal during glaucoma surgery. Injection of viscoelastic is also used to dissect tissues such as the lens capsule or retinal membranes.
Viscoelastics are typically delivered to tissues with a syringe under manual control by the surgeon. A hand operated syringe is used to inject the viscoelastic through a needle or cannula attached onto a distal luer connector of the syringe. Due to the high viscosity of the material, it is often difficult to manually produce sufficient force with a syringe, especially with small bore cannulas or needles. In addition, the dynamic flow nature of viscoelastic materials makes it difficult to deliver small amounts in a precise, controlled manner.
The present invention is related to a means for improved delivery of high viscosity materials through a cannula or needle into tissues.